Apparatus and a method for calibration of an industrial robot

ABSTRACT

An apparatus for calibration of an industrial robot, the apparatus comprising a body ( 7 ) having a first angle-measuring member ( 10 ) arranged for measuring an angle relative to the vertical line about a first measuring axis ( 12 ) and mouting means ( 8, 9, 25 ) for mounting the body to the robot during the calibration. The apparatus comprises a second angle-measuring member ( 11 ) arranged for measuring an angle relative to the vertical line about a second measuring axis ( 13 ) differing from the first measuring axis. A method for calibration of an industrial robot having a plurality of sections movably connected to each for rotation about a plurality of axes, using an apparatus according to claim 1 or 2, the method comprising: attaching the body ( 7 ) to a section of the robot, reading an angle measurement from the first angle-measuring member ( 10 ), moving the robot about a first axis in dependence of said angle measurement for the first angle-measuring member ( 10 ), reading an angle measurement from the second angle-measuring member ( 11 ), and moving the robot about a second axis in dependence of said angle measurement from the second angle-measuring member ( 11 ).

FIELD OF THE INVENTION

[0001] The present invention relates to an apparatus for calibration ofan industrial robot, the apparatus comprising a body having a firstangle-measuring member arranged for measuring an angle relative to thevertical line about a first measuring axis and mounting means formounting the body to the robot during the calibration. The presentinvention also relates to a system for robot calibration comprising anindustrial robot and an apparatus for calibration of the industrialrobot. The present invention further relates to a method for calibrationof an industrial robot having a first and a second axis. The presentinvention also relates to a computer program product in connection withthe calibration of an industrial robot.

PRIOR ART

[0002] An industrial robot can be viewed as a chain of sections movablyconnected to each other. Two adjacent sections are joined to each otherso that they either are rotatable relative to each other about arotational axis or linearly displaceable relative to each other. Thefirst section in the chain is the base of the robot and the last sectionusually constitutes a tool attachment. For the possibility to determinethe position of the robot, each joint usually is provided with anangle-measuring device in the form of an encoder or a resolverindicating the position of the joint relative to a zero position. Beforean industrial robot can be used it must be calibrated, which means thateach of the angle-measuring devices is calibrated with reference to thezero position. The robot is calibrated in the production plant before itis delivered and sometimes on site before being set to work. Thereafter,the robot is calibrated after larger repairs such as motor or armchanges or after collisions.

[0003] In the patent document U.S. Pat. No. 5,239,855, a known method ofcalibration is shown, in which an inclinometer or some other type ofinstrument for measuring the inclination is used to calibrate theangle-measuring devices. An inclinometer measures the angle between anobject and the vertical line and is, for example, an electronic spiritlevel. The inclinometer is placed on a plane of reference on one of thesections, and generates a signal, which is a measure of the anglebetween the plane of reference of the section and the vertical line.Thereafter, the joint is moved in dependence of the generated signaluntil it has a predetermined angle relative to the vertical line. Theother sections are calibrated in the same way.

[0004] The placement of the planes of reference against which thecalibration device is to be attached is predetermined. The planes ofreference consists of accurately machined surfaces to obtain a highdegree of flatness. When the robot is to be calibrated, it is moved to apredetermined calibration configuration. In this configuration, at leastone of the sections is usually oriented in a direction, which differsfrom the directions of the other sections. Usually, the angles betweenthe length axes of the sections are approximately 90°. Thus, the planesof reference may have different directions depending on which section tobe calibrated. The planes of reference are usually either horizontal orvertical during the calibration.

[0005] A problem with said method of calibration is that theinclinometer must be mounted on the planes of reference of the robotwith a very high precision. The inclinometer is first put on aninclinometer plate, which is then mounted on an adapter plate. Theadapter plate is then attached to the plane of reference. Depending onthe direction of the plane of reference to be calibrated, todaydifferent adapter plates are used. Usually, one type of adapter plate isused for horizontal planes of reference and another type of adapterplate is used for vertical planes. This way of attaching theinclinometer to the robot includes a large number of sources of error.Examples of sources of error are mounting errors between the adapterplate and the plane of reference of the robot, mounting errors betweenthe inclinometer plate and the adapter plate, and errors of tolerance ofthe adapter plate. The fact that several different adapter plates areused also contributes to increasing the mounting error.

[0006] An apparatus for calibration of an articulated robot is shown inU.S. Pat. No. 4,505,049. The calibration apparatus comprises aninclinometer provided on an inclinometer plate, which is mounted on onesidepiece of an L-shaped adapter plate. The other sidepiece of theL-shaped adapter plate has a flat surface adapted for being in contactwith the plane of reference during the calibration. The flat surface ofthe adapter plate is provided with positioning means projecting from thesurface and is adapted to fit in with corresponding receiving meansformed in the plane of reference. The object of the positioning means isto establish a definitely determined positional relation between thesurface and the plane of reference.

[0007] A common type of industrial robot comprises a base adapted forresting on a horizontal foundation and a stand, which is rotationallyarranged relative to the base about a first vertical axis. Since thefirst axis is essentially parallel with the vertical line, it cannot becalibrated with an inclinometer attached to the stand. Accordingly, asecond problem with the method of calibration described above is that itcannot calibrate rotational axes parallel with the vertical line.

SUMMARY OF THE INVENTION

[0008] The present invention has been developed to obviate theabove-described disadvantages of the prior art and has as its object theprovision of an apparatus and a method and a computer program productfor calibration of an industrial robot, wherein the error during themounting of the body on the plane of reference is reduced.

[0009] The apparatus according to the present invention is characterisedin that the apparatus comprises a second angle-measuring member arrangedfor measuring an angle relative to the vertical line about a secondmeasuring axis differing from the first measuring axis. By having twoangle-measuring members arranged with an angle relative to each other,it is possible to calibrate in two directions without having to rotatethe angle-measuring member. Advantageously, the second angle-measuringmember is arranged essentially perpendicularly to the firstangle-measuring member. This means that two axes being perpendicular toeach other can be calibrated without reorientation of the body. This isadvantageous, for example when the wrist axes are to be calibrated, i.e.the axes 3, 4, 5, and 6, for a robot having six axes. When the robot isin its predetermined calibration configuration, the axes 4 and 6 areparallel to each other and the axes 3 and 5 are perpendicular to theaxes 4 and 6. During the calibration of the wrist axes, the body isplaced on the outermost section, which is usually a tool attachment.Thanks to the fact that the body comprises two angle-measuring membersarranged perpendicularly to each other, all four axes can be calibratedwithout moving the body.

[0010] According to an embodiment of the invention, the mountingarrangement comprises three protruding contact elements being arrangedso that the body is in contact with the plane of reference through saidcontact elements during the calibration. The calibration apparatus andthe robot are connected to each other through the contact elements. Byusing three contact elements the contact area between the calibrationapparatus and the plane of reference is reduced without reducing thestability in the connection. By reducing the contact area between thecalibration apparatus and the robot, the mounting error is reduced aswell. With three contact elements, there are at least three contactpoints between the body and the plane of reference of the robot, whichmeans that the angle-measuring member and the robot are fixed relativeto each other with at least three degrees of freedom. A stableattachment of the body against the robot is thus obtained. Bypositioning the contact elements so that they form corners of a trianglemaximum stability is achieved.

[0011] According to an embodiment of the invention, each of the contactelements comprises a flat portion adapted for being in contact with theplane of reference during the calibration. From a manufacturing point ofview it is an advantage to make the portion adapted for being in contactwith the plane of reference flat.

[0012] According to a further embodiment of the invention, the mountingarrangement further comprises an attachment element for attaching thebody to the plane of reference. Preferably, the attachment element is ascrew. Thereby, a reliable and inexpensive attachment is obtained.Further, the screw and a corresponding hole in the plane of referencefacilitates the positioning of the body relative to the plane ofreference.

[0013] According to a further embodiment of the invention, the apparatusfurther comprises a mounting member for pivotally connecting the body tothe robot. By this arrangement, it is possible to calibrate anessentially vertical axis of the robot by mounting the body to the robotsuch that the body, including the angle-measuring member, forms apendulum. Hence, it will be possible to calibrate all the axes of therobot using one single body. In a further embodiment, the mountingmember comprises a shaft having with an attachment element for attachingthe shaft to the robot, the body being arranged pivotal about thatshaft.

[0014] According to a further embodiment of the invention, the apparatuscomprises a calibration element for mounting to the robot and the bodycomprises a portion adapted for being in contact with said calibrationelement during calibration. The robot comprises a first and a secondsection, the second section being coupled to the first section forrotation about an essentially vertical axis through the first section.For calibration of the vertical axis through the first section, the bodyis mounted to the second section and the calibration element is mountedto the first section. The robot is moved until the portion of the bodyis in contact with the calibration element mounted on the first section.When the second section is moved further, the calibration element pushesthe body so that it pivots about the shaft, thus causing an angularchange of the angle-measuring member. Since the signal from theangle-measuring member depends on the relative position between thefirst and the second section, it is possible to calibrate the verticalaxis through the first section.

[0015] According to a further embodiment of the invention, the body isshaped so that its centre of gravity is displaced in relation to an axisthrough said mounting member and said portion adapted for being incontact with said calibration element. Thanks to the fact that thecentre of gravity is displaced in relation to that axis, the measuringaxis deviates from the vertical line when the body is moved into contactwith the calibration element and thus it is possible to measure on bothsides of the vertical line. The size of the displacement determines thesize of the angular interval possible to measure before the measuringaxis coincides with the vertical line.

[0016] According to a further embodiment of the invention, the body isessentially L-shaped having a first and a second branch arrangedessentially perpendicularly to each other, said mounting member and saidportion being located at or in the vicinity of the first branch. Such abody has a centre of gravity, which is displaced in relation to an axisthrough said mounting member and said portion adapted for being incontact with said calibration element when said mounting member ismounted to the stand of the robot.

[0017] According to a further embodiment of the invention, the bodycomprises a second mounting arrangement for mounting the body to asecond plane of reference on the robot, said second mounting arrangementbeing arranged in an angle relative to the first mounting arrangement,said angle essentially corresponding to the angle between two planes ofreference of the robot when the robot is in its calibrationconfiguration. With such a second mounting arrangement, the same bodycan be used for calibration of planes of reference being arranged in twodifferent directions. Accordingly, there is no need for using differentcalibration bodies or different adapter plates, such as in the priorart, for measuring two planes of reference with different anglesrelative to the vertical line. The consequence of this is that a sourceof error, which is difficult to master during calibration, directlydisappears. The second mounting arrangement is preferably arrangedessentially perpendicularly to the first mounting arrangement. If themounting arrangements are arranged perpendicularly against each other,both horizontal and vertical planes of reference can be measured withthe same body.

[0018] According to a further embodiment of the invention, the firstmounting arrangement comprises key means adapted for cooperation withcorresponding key means on the first plane of references, and the secondmounting arrangement comprises key means adapted for cooperation withcorresponding key means on the second plane of reference, the key meansof the first mounting arrangement differing from the key means of thesecond mounting arrangement. The key means ensures that an operatorattaches the body to the right calibration plane and in a rightposition. Thus, the key-means prevents the operator from by mistakemounting the body to the plane of reference in a wrong way. Since thebody is provided with two mounting arrangements, there are twopossibilities to mount the body on the plane of reference, but only oneis correct. The key means of a certain plane of reference only fits inwith the correct mounting arrangement and thus misplacement is avoided.

[0019] According to a further embodiment of the invention, each keymeans of the mounting arrangements comprises at least two protrudingelements adapted to fit in with corresponding notches in the plane ofreference and that the distance between the protruding elements differsbetween the first mounting arrangement and the second mountingarrangement.

[0020] According to a further embodiment of the invention, each keymeans of the mounting arrangements comprises at least one protrudingelement adapted to fit in with a corresponding notch in the plane ofreference, and the key-means have different shape, such as wedge-shapedor quadrangular. The protruding elements can for instance differ byhaving different diameters or height.

[0021] According to a further embodiment of the invention, each keymeans of the mounting arrangements comprises at least one protrudingelement adapted to fit in with a corresponding notch in the plane ofreference, and the key-means of the first and the second mountingarrangement have different shape. Preferably, the protruding element hasan asymmetrical shape so that it only fits in one position relative tothe corresponding notch.

[0022] According to a further embodiment of the invention, the robot isconnected to a control system via a cabling member adapted fortransferring power and signals between the robot and the control systemand the apparatus comprises a junction member electrically connected tothe angle-measuring member, the junction member being provided with aconnector for connection to said cabling member and means fortransferring power to the angle-measuring member and transferringmeasurement values from the angle-measuring member via said cablingmember. By such an arrangement, the cable member being used fortransferring power and signals between the robot and the control systemcan also be used for transferring power and signals between the controlsystem and the angle-measuring member. An advantage with thisarrangement is that the robot does not have to be provided with anyextra cable for the calibration. By providing the calibration apparatuswith such a junction member, the expenses in connection with providingeach robot with an extra cable is avoided.

[0023] The method according to the present invention comprises:attaching the body to a section of the robot, reading an anglemeasurement from the first angle-measuring member, moving the robotabout a first axis in dependence of said angle measurement from thefirst angle-measuring member, reading an angle measurement from thesecond angle-measuring member, and moving the robot about a second axisin dependence of said angle measurement from the second angle-measuringmember.

[0024] According to an embodiment of the invention, the method furthercomprises: attaching the body to a section of the robot, reading anangle measurement from the first angle-measuring member, moving therobot about a first axis in dependence of said angle measurement fromthe first angle-measuring member, reading an angle measurement from thesecond angle-measuring member, and moving the robot about a second axisin dependence of said angle measurement from the second angle-measuringmember.

[0025] The computer program product according to the invention comprisesa computer-readable medium, having thereon a computer readable programmeans which, when run on a computer, makes the computer performcalibration of an industrial robot with the calibration apparatusaccording to the invention, including receiving an angle measurementfrom the first angle-measuring member, sending control signals to therobot about moving a first axis of the robot in dependence of said anglemeasurement from the first angle-measuring member, receiving an anglemeasurement from the second angle-measuring member, and sending controlsignals to the robot about moving a second axis in dependence of saidangle measurement from the second angle-measuring member. Thus, thecalibration is made automatically and therefore becomes more precise andaccurate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will now be explained by differentembodiments described as examples with reference to the appendeddrawings.

[0027]FIG. 1 shows an industrial robot in a calibration configurationhaving a calibration apparatus according to the invention mountedthereupon.

[0028]FIG. 2 is in a perspective view showing an embodiment of acalibration apparatus according to the invention.

[0029]FIG. 3 is a perspective view showing how the angle-measuringmembers are positioned relative to each other in the calibrationapparatus.

[0030]FIG. 4a is a side view showing a first side of the calibrationapparatus in FIG. 2.

[0031]FIG. 4b is a side view showing a second side of the calibrationapparatus in FIG. 2.

[0032]FIG. 5 is a sectional view showing the calibration apparatus andthe plan of reference of the robot during calibration.

[0033]FIGS. 6a-6 c are perspective views showing the body and the robotduring calibration of an essentially vertical axis.

[0034]FIG. 7 shows the electrical connection of the calibrationapparatus according to an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

[0035]FIG. 1 shows an example of an industrial robot standing in acalibration configuration. The robot comprises a base 1, which is firmlymounted on a foundation. The robot further comprises a stand 2, which isrotatable relative to the base 1 around a first vertical axis. In thetop end of the stand 2, a first robot arm 3, is rotatably mounted abouta second horizontal axis. In the outer end of the first arm 3, a secondarm 4 is rotatably mounted relative to the first arm about a third axis.The second robot arm 4 comprises two parts, 4 a and 4 b, and the outerpart 4 b being rotatable relative to the inner part 4 a around a fourthaxis coinciding with the longitudinal axis of the second arm 4. In itsouter end, the second arm 4 supports a so-called robot hand 5, which isrotatable about a fifth axis, which is perpendicular to the length axisof the second arm 4. The robot also comprises a tool attachment 6. Theouter part of the robot hand with the tool attachment 6, is rotatablerelative to the inner part of the robot hand about a sixth axis. Foreach of the axes of the robot, there is a level indicator giving asignal, which is a measure of the present rotational angle of the axis.The output signal from the level indicator is transmitted to a controlsystem of the robot.

[0036] When the robot is in its calibration configuration, the axis ofthe robot are in their calibration position, as shown in FIG. 1, thefirst arm 3 is placed parallel with the first axis, i.e. parallel withthe vertical line, the second arm 4 is placed perpendicular to the firstarm 3 and the robot hand 5 is placed parallel with the length axis ofthe second arm, i.e. perpendicular to the vertical line. On anindustrial robot, there is usually a plurality of especially formedplanes of reference intended for being used during calibration of therobot. In FIG. 1, a body 7 according to the invention is shown arrangedon some of these planes of reference. A first plane of reference on therobot is arranged on the base 1, a second plane of reference is arrangedon the first arm 3, a third plane of reference is arranged on the secondarm 4, and a fourth and last plane of reference is arranged on the toolattachment 6.

[0037] The fourth plane of reference may also be provided on adetachable plate attached to the tool during the calibration.

[0038] FIGS. 2 show an embodiment of a calibration apparatus accordingto the invention. The apparatus comprises a body 7 having a first and asecond mounting arrangement 8, 9 for mounting the body to the planes ofreference of the robot. The body further comprises two angle-measuringmembers 10, 11 in the form of inclinometers measuring the angle of anobject relative to the vertical line. An inclinometer functions as anelectronic level and measures the inclination angle about a measuringaxis. The inclinometers 10, 11 are positioned with their measuring axes12, 13 perpendicular to each other. FIG. 3 shows the angle-measuringmembers 10, 11 in more detail.

[0039] The body 7 is essentially L-shaped having a first and a secondbranch 7 a, 7 b arranged essentially perpendicularly to each other. Thefirst mounting arrangement 8 is mounted on a surface of the first branch7 a and the second mounting arrangement 9 is mounted on a surface of thesecond branch 7 b. Accordingly, the mounting arrangements are arrangedperpendicularly to each other. The first angle-measuring member 10 ispositioned with its measuring axis 12 essentially parallel to thesurface of the first branch 7 a and perpendicularly to the surfacesecond branch 7 b. The second angle-measuring member 11 is positionedwith its measuring axis 13 essentially perpendicularly to the surface ofthe first branch 7 a and parallel to the surface second branch 7 b.

[0040]FIG. 4a shows a front view of the surface of the first branch 7 a.The first mounting arrangement 8 comprises three protruding contactelements 15 adapted for being in contact with the plane of referenceduring the calibration, an attachment element 17 for removably attachingthe body to the plane of reference and key means 19 adapted for fittingin with corresponding key means on the plane of references. The contactelements 15 are arranged so that the body 7 is in contact with the planeof reference through the contact elements during the calibration. Inthis embodiment, the contact elements 15 are cylindrical and one endthereof fixedly connected to the surface of the body and the other endflat and intended to bear on the surfaces of the plane of reference oron a plate having a corresponding function, which plate is mounted onthe robot. The three contact elements 15 are arranged as the corners ofa triangle.

[0041] In a preferred embodiment, the attachment element 17 is a screwintended to be attached to a corresponding hole with threads provided inthe plane of reference. Alternatively, a magnet, a spring arrangement ora bayonet may be used as an attachment element. The key means 19comprises two protruding elements adapted to fit in with correspondingnotches in the plane of reference. The distance d₁ between theprotruding elements is the same as the distance between thecorresponding notches in the plane of reference. The body shall bedifferently orientated depending on which of the calibration plans thebody shall be mounted to. The key means helps the robot operator toposition the body correctly to the plane of reference.

[0042]FIG. 4b shows a front view of the surface of the second branch 7b. The second mounting arrangement 9 comprises three protruding contactelements 20, an attachment element 21, and key means 22 arranged in thesame manner as in the first mounting arrangement 8. The distance d₂between the protruding elements 22 of the second mounting arrangement 9differs from the distance d₁ between the protruding elements 19 of thefirst mounting arrangement 8. Hence, it is impossible to mount themounting arrangement to the wrong plane of reference and accordingly thebody will always be correctly orientated. The first mounting arrangement8 fits in with the first and the third plane of reference and the secondmounting arrangement 9 fits in with the second and the fourth plane ofreference. For small robots, it is possible to reduce the number ofplanes of reference to only three. The third, fourth, fifth, and sixthaxis can be calibrated using the same plane of reference, e.g. the planeof reference of the tool attachment 6.

[0043]FIG. 5 shows how the first branch 7 a of the body is mounted to aplane of reference 23 of the robot. The contact elements 15 are bearingon the flat surface of the plane of reference, the screw 17 is engagedto a corresponding hole in the plane of reference, and the protrudingelements 19 of the key means are recessed in corresponding notches 24 inthe plane of reference 23.

[0044] During the calibration process, the body 7 is attached throughthe first mounting arrangement to the plane of reference on the base 1of the robot. Reference angles are read from the first and the secondangle-measuring member. The reference angles are stored in the controlsystem of the robot. Thereafter, the axes 26 are calibrated byattachment of the body 7 to the other planes of reference, reading anyof the inclinometers and calculating the difference between the readangle and the angle of reference of that inclinometer. This calculationis performed in the control system of the robot. Thereafter, the controlsystem orders the axis being calibrated to move in dependence of thecalculated difference until the difference has a predetermined value andthe axis ends up in its calibration position. Usually, the predeterminedvalue of the difference is zero. During calibration of the wrist axes,i.e. the axes 5 and 6, the body 7 is attached by the second mountingarrangement to the tool attachment 6. Thus, the same body can be used tocalibrate axes, which are perpendicular to each other.

[0045] The axes 2-6 of the robot are possible to calibrate with the bodyattached to the planes of reference. But the first axis of the robot,which axis is parallel to the vertical line, is not possible tocalibrate in the same manner. For calibration of the first axes of therobot, the calibration apparatus is provided with a mounting member 25for pivotal connection of the body 7 to the stand 2 of the robot. Themounting member 25 comprises a shaft 27, an attachment element forattaching the shaft 27 to the stand 2. The attachment element comprisesa tapering part 28 and a screw 29 adapted to fit in with a correspondinghole in the stand 2. The body is arranged pivotally about the shaft 27.

[0046] The shaft 27 is located in a through-hole in the first branch 7 aof the body 7. The axis 30 of the shaft 27 is arranged perpendicular tothe measuring axis 12 of the first angle-measuring member 10. Thecalibration apparatus further comprises a calibration element formounting to the base 1 of the robot and the body comprises an elongatedprotruding portion 32 adapted for being in contact with said calibrationelement during calibration of the first axis. The portion 32 is locatedin the outer corner connecting the first and the second branch of thebody. The longitudinal axis of the portion 32 is parallel to the axis 30of the shaft 27. In another embodiment, the portion 32 consists of a rodpositioned in a recess in the body 7.

[0047]FIG. 6a shows the calibration apparatus when it is used forcalibration of the first axis of the robot. The body 7 is pivotallyattached to the stand 2 of the robot through the shaft 27. An elongatedcalibration element 35 is mounted to the base 1 of the robot. Thecalibration element 35 is vertically positioned on the base. Thecalibration element 35 is arranged such that it is removable from thebase after the calibration has been carried out. Due to the L-shape ofthe body, the centre of gravity of the body is displaced in relation toan axis through the mounting member 27 and the portion 32. Thedisplacement is about 5 mm. Therefore, the surface of the first branch 7a is not vertical when the body is connected to the stand 2 andconsequently the measuring axis 13 of the second inclinometer 11 is notvertical. Thus, the measuring angle differs from the vertical line.

[0048] The calibration of the first axes is illustrated in FIGS. 6a-6 c.To begin with, the calibration element 35 is mounted to the base 2 andthe body is attached to the stand 2 by attaching the mounting member 25to the stand 2. The stand 2 is then moved to a rough calibrationposition, i.e. a position close to the calibration position. A roughcalibration position is within 10° from the actual calibration position.At wider angles, the inclinometers may not work properly. The anglemeasurements from the first inclinometer 10 are read during thecalibration. The angle measurements correspond to the angle between themeasuring axis 12 and the vertical line. Thereafter, the stand 2 ismoved about the first axis until the body is in contact with thecalibration element 32 and the stand 2 is further moved in response tosaid measured angle until the first axis is calibrated, i.e. the axisends up in its calibration position. As shown in the FIGS. 6a-6 c thebody 6 functions as a pendulum rotating about a horizontal axis duringthe calibration of the first axis.

[0049] In an embodiment of the invention, the calibration is controlledby software in the control system of the robot. The control systemreceives signals from any of the inclinometers, which signals correspondto the angle between the measuring axis of the inclinometer and thevertical line. The software produces control signals in response to thereceived signals from the inclinometer and then sends the controlsignals to the robot. The robot is moved in accordance with the receivedcontrol signals until the axis is in its calibration position. Thismethod is repeated for each axis until all the axes of the robot arecalibrated. The control system comprises necessary equipment, such as aprocessor, memory, and I/O units, for running the software, whichperforms the calibration.

[0050]FIG. 7 shows a robot 40 connected to a control unit 42 comprisingthe control system of the robot. The control unit 42 is coupled to therobot via a cabling member 44 adapted for transmitting signals and databetween the robot 40 and the control unit 42 and for transmitting powerto the robot. The calibration apparatus according to an embodiment ofthe invention comprises a junction member 46 electrically connected tothe angle-measuring members 10, 11 of the body 7 via two cables 47, 48.The junction member 46 comprises a first connector 49 for connection ofthe cabling member 44 to the control unit 42, a second connector 50 forconnection of a second cabling member 51 to the robot 40 and aseries-measuring card adapted for transmitting power to theangle-measuring member and transmitting measurement values from theangle-measuring members via the cabling member 44 to the control system.

[0051] During normal operation of the robot, the control unit 42 isconnected to the robot 40 via the cabling member 44, which is connectedto the robot. During calibration of the robot, the control unit 42 isconnected to the robot 40 via the cabling member 44, the junction member46 and the cabling member 51. The angle-measuring members of the body 7are supplied with power and signals are transmitted to the control unitvia the cabling member 44, the junction member 46 and the cables 47 and48.

[0052] The present invention is not limited to the embodiments disclosedbut may be varied and modified within the scope of the following claims.The robot may in some applications be mounted at the ceiling, with thebase located above the stand. The calibration apparatus of the presentinvention can be used for calibration of the first axis when the robotis mounded upside down, if the body and the calibration element areattached to each other by any resilient means, such as a rubber band,for avoiding that the body rotates due to the gravity.

[0053] The body may have different shapes, but should preferablecomprise two flat plan, for example the body can be cubical.

[0054] It is also possible to provide the base with more than onecalibration element. If it is difficult to reach the calibration elementduring the calibration it is advantageous to have a plurality ofcalibration element to chose between. The calibration element may eitherbe removable or fixtly mounted. The calibration element may consist of amachined portion of the base.

[0055] In another embodiment, the body is used as a pendulum forcalibration of the non-vertical axes as well as the vertical axes of therobot. In this embodiment the calibration element and the body ismounted on the same section during calibration. This embodiment isadvantageous since it is sufficient to provide the body with onemounting means, the pivotal mounting member.

[0056] The order in which the axes are calibrated could of course bedifferent from the order described above, for example the first axis maybe calibrated before the other axes.

[0057] The present invention is also useful for parallel cinematicmanipulators.

1. An apparatus for calibration of an industrial robot, the apparatuscomprising a body having a first angle-measuring member arranged formeasuring an angle relative to the vertical line about a first measuringaxis and mounting means for mounting the body to the robot during thecalibration, further the apparatus comprises a second angle-measuringmember arranged for measuring an angle relative to the vertical lineabout a second measuring axis differing from the first measuring axiswherein said mounting means comprises a first mounting arrangement formounting the body to a plane of reference of the robot, the mountingarrangement comprising three protruding contact elements being arrangedso that the body is in contact with the plane of reference through saidcontact elements during the calibration, and wherein said mounting meanscomprises a second mounting arrangement for mounting the body to asecond plane of reference on the robot, that said second mountingarrangement is arranged in an angle relative to the first mountingarrangement and that said angle essentially corresponds to the anglebetween two planes of reference of the robot when the robot is in itscalibration configuration.
 2. The apparatus according to claim 1,wherein the second angle-measuring member is arranged with its measuringaxis essentially perpendicular to the measuring axis of the firstangle-measuring member.
 3. The apparatus according to claim 1, whereineach of the contact elements comprises a flat portion adapted for beingin contact with the plane of reference during the calibration.
 4. Theapparatus according to claim 1, wherein the contact elements arearranged so that they form corners of a triangle.
 5. The apparatusaccording to claim 1, wherein the mounting arrangement comprises anattachment element for attaching the body to the plane of reference. 6.The apparatus according to claim 4, wherein the attachment element is ascrew.
 7. The apparatus according to claim 1, wherein the first mountingarrangement is arranged in a first plan and the second mountingarrangement is arranged in a second plane being essentiallyperpendicular to the first plan.
 8. The apparatus according to claim 1,wherein the first mounting arrangement comprises key means adapted forcooperating with corresponding key means on the first plane ofreferences, that the second mounting arrangement comprises key meansadapted for cooperating with corresponding key means on the second planeof reference, and that the key means of the first mounting arrangementdiffers from the key means of the second mounting arrangement.
 9. Theapparatus according to claim 8, wherein each key means of the mountingarrangements comprises at least one protruding element adapted to fit inwith a corresponding notch in the plane of reference, and the key-meansof the first and the second mounting arrangement have different shape.10. The apparatus according to claim 8, wherein each key means of themounting arrangements comprises at least two protruding elements adaptedto fit with corresponding notches in the plane of reference and that thedistance between the protruding elements differs between the firstmounting arrangement and the second mounting arrangement.
 11. Theapparatus according to claim 1, wherein the mounting means comprises amounting member for pivotally connecting the body to the robot.
 12. Theapparatus according to claim 11, wherein said mounting member comprisesa shaft having an attachment element for attaching the shaft to therobot, the body being arranged pivotal about that shaft.
 13. Theapparatus according to claim 11 or 12, wherein the apparatus comprises acalibration element for mounting to the robot and the body comprises aportion adapted for being in contact with said calibration elementduring calibration.
 14. The apparatus according to claim 13, wherein thebody is shaped so that its center of gravity is displaced in relation toan axis through said mounting member and said portion adapted for beingin contact with said calibration element.
 15. The apparatus according toclaim 13, wherein the body is essentially L-shaped having a first and asecond branch essentially perpendicular to each other, said mountingmember and said portion being located at or in the vicinity of the firstbranch.
 16. The apparatus according to claim 1, wherein the robot isconnected to a control system via a cabling member adapted fortransferring power and signals between the robot and the control system,wherein the apparatus comprises a junction member electrically connectedto the angle-measuring member, the junction member being provided with aconnector for connection to said cabling member and means fortransferring power to the angle-measuring member and transferringmeasurement values from the angle-measuring member via said cablingmember.
 17. A method for calibration of an industrial robot having aplurality of sections movably connected to each for rotation about aplurality of axes, using an apparatus according to claim 1, the methodcomprising: attaching the body to a section of the robot, reading anangle measurement from the first angle-measuring member, moving therobot about a first axis in dependence of said angle measurement fromthe first angle-measuring member, reading an angle measurement from thesecond angle-measuring member, and moving the robot about a second axisin dependence of said angle measurement from the second angle-measuringmember.
 18. The method for calibration of an industrial robot accordingto claim 17, comprising: providing the robot with a protrudingcalibration element, pivotally attaching the body to a section beingmovable about an essentially vertical axis, moving the section aboutsaid vertical axis until the body is in contact with the calibrationelement, reading an angle measurement from the first angle-measuringmember, and moving the section about said vertical axis in dependence ofsaid angle measurement from the first angle-measuring member.
 19. Themethod for calibration of an industrial robot according to claim 17,wherein the step of attaching the body to a section of the robotcomprises: bringing the contact elements of the calibration body intocontact with a plane of reference on the robot, and attaching thecalibration body to the plane of reference.
 20. A computer programproduct comprising a computer readable medium, having thereon a computerreadable program means which, when run on a computer, makes the computerperform calibration of an industrial robot with a calibration apparatusaccording to claim 1, the computer program means comprising computerprogram instructions executable by a process for performing the stepsof: receiving an angle measurement from the first angle-measuringmember, sending control signals to the robot about moving a first axisof the robot in dependence of said angle measurement from the firstangle-measuring member, receiving an angle measurement from the secondangle-measuring member, and sending control signals to the robot aboutmoving a second axis in dependence of said angle measurement from thesecond angle-measuring member.